Knit with Bex

You're correct. If properly prepared and stored in an airtight container, the stock solution can be used for quite a long time. I have actually used three year old stock to successfully start a new vat. Many traditional vat dyers keep a continual indigo dye vat going for 20+ years. The sludge build-up has to be dredged out every so often, but it is possible and conserves indigo dye.